Organo-silicon polymers and methods of preparing them



Patented Jan. 27, 1948 UNITED STATES PATENT orrica ORGANO-SILICONPOLYMERS AND METHODS OF PREPARING THEM Rob Roy McGregor, Verona, andEarl Leathen Warrick, Pittsburgh, Pa., assignors to Corning Glass Works,Corning, N. Y., a corporation of New York No Drawing. Application March30, 1943,

Serial No. 481,142

fiClaims. (crest-46.5)

This invention relates to new compositions of matter, their preparationand uses and, more particularly, to org'ano-silicon polymers and methodsof preparing them. I

This application is a continuation-in-part of our copending applicationSerial Number 460,830,.

filed October-5,1942.

The present invention is concerned with a method of further polymerizingorgano-silicon oxid polymers and with the products derived therefrom.Organo-silicon oxide polymers are compounds which contain organicradicals attached to silicon through a carbon atom and whose siliconatoms are joined to other silicon chloride or ethyl orthosilicate, maybe included;

along with thehydrolyzable organo-silicanes.

By hydrolyzable organo-silicanes we mean de-' rlvatives of SiH4 whichcontain readily hydrolyzable radicals such as hydrogen, halogens, aminogroups, alkoxy, aroxy and acyloxy radicals, etc, the remaining valencesof the silicon atoms being satisfied by organic radicals that are joinedto the silicon atoms through carbon atoms such as alkyl, substitutedalkyl, aryl, substituted aryl radicals, etc.

Hydrolysis of the above silicanes or mixtures thereof is generallyconcurrently accompanied by condensation to a greater or less degreedepending upon the conditions of hydrolysis and the particular silicanesinvolved. As a result of the hydrolysis and concurrent condensation,organesilicon oxide polymers or organo-siloxanes (as they are nowcommonly called) are produced which are partially or completelycondensed and which have on the average up to and includin three organicradicals attached to each silicon atom. The polymers so obtained vary incharacter, some being oily liquids, others being crystalline solids orgels. They also vary in the ease with which they may be furtherpolymerized by plete hydrolysis and condensation. Those which are onlypartially condensed may be converted to higher polymers and eventoapproach complete condensation are extremely resistant to furtherpolymerization by heat alone. These substantially completely condensedpolymers are not limited to those which are of high molecular weight butmaybe polymers of low molecular weight as well. For example, thecondensed hydrolysis products of the di-organosilicanes are essentiallycompletely condensed even in the low polymeric stages and existgenerally as liquids in the trimeric form with polymers as high as thehexamer being reported in only rare instances. Since the higher polymersof these organo-silicon oxide compounds, and

particularly the higher polymers of the substantially completelycondensed compounds, have been found to possess properties which adapt"them to many, industrial applications as will be described below, it ishighly desirable to provide a method of further polymerizing theorganosilicon oxide polymers to higher polymeric compositions,that'is,=to increase their average mo lecular weight.

- The primary object of this invention is to provide a )method ofpolymerizing the hydrolysis products of hydrolyzable 'org'ano-silicanesor mix-- -tures thereof. 1

Another object of our invention is to provide a method of furtherpolymerizing an organohydrolyzable atom or group.

Still'another object of the present invention is to provide a method ofpolymerizing a substantiall completely condensed liquid hydrolysisproduct of a mixture comprising essentially a diorgano-substitutedsilicane to a polymeric composition which is substantially free ofpolymers having less than seven silicon atoms per molecule.

Another object of our invention is to provide a method oi'polymerizingto a heat convertible state a liquid organo-siloxane having on theaverage less than three organic radicals attached through carbon atomsto each silicon atom.

solids by heat i alone or even by standing' at room temperature 'byvirtue of the completion ofcondensation. On the other hand, thoseorgano-siloxanes which A further object of our invention is to provide amethod of polymerizing to an infusible resinous solid a liquidorgano-siloxane having on the average less than three organic radicalsattached through carbon atoms to each silicon atom.

Another object of our invention is to prepare organo-siloxanes of highaverage molecular weight which are heat convertible and soluble inorganic solvents.-

A still further object of our invention is to prepare organo-siloxanesof high average molecular weight which are tack-free resins.

In accordance with our invention, we have provided a method of preparingan extremely useful polymeric composition from the hydrolysis product ofa hydrolyzable organo-silicane or of a mixture of hydrolyzableorgano-silicanes which comprises maintaining phosphorus pentoxide orphosphoric acid in intimate and continuous contact with the hydrolysisproduct under polymerizing conditions until a polymeric compositionhaving the properties desired is obtained. If desired, the phosphoruspentoxide or the phosphoric acid may be added during the initialhydrolysis and condensation of the silicane or mixture of silicanes. Itis important in the case of the liquid hydrolysis products which aresubstantially completely condensed, that the catalyst be maintained inintimate and continuous contact with the siloxane until the desiredhigher polymer is obtained; for we have found that an appreciableincrease in average molecular weight does not occur until the polymerhas been treated for some time. After this induction period, theviscosity and average molecular weight of the treated material risesrapidly until a stage of polymerization is reached where the catalyst isno longer necessary to promote further polymerization but heat alone in'the presence of air is sutficient to convert the polymerized siliconeto a tack-free resinous solid. Those organo-siloxanes which areinitially only partially condensed do polymerize by heat alone but wehave found that treatment in accordance with our invention not onlyincreases the rate of polymerization but in many instances producesflexible resinous solids instead of the me.- chanically weak gelsordinarily obtained by heat alone. In carrying out the polymerization,we have found that the addition of water, preferably in the form ofsteam, aids in speeding up the polymerization. The particularconcentration and quantity of acid employed and the optimum temperaturefor carrying out the polymerization are conditions which vary with thesiloxane being treated and also with the type of polymer desired as willbe readily apparent from the examples given below. In general, we preferto employ phosphoric acid having a concentration of about 85% and tocarry out the polymerization at a temperature within the range of fromabout 100 C. to about 250 C.

In general, any liquid organo-siloxane having on the average less thanthree organic radicals attached through carbon atoms to each siliconatom may be polymerized by our method; that is, treatment in accordancewith our method will result in an increase in average molecular weight.Our method is not generally applicable to those siloxanes having threeorganic radicals attached to each silicon atom, namely, the dimericethers,

since the only way the latter can further polymerize is by removal ofgroups. It is to be understood, however, that treatment by our methodmay result in loss of some groups but it is believed that polymerizationis primarily due to rearrangement of the Si-O-Si bonds. By our method,liquids of extremely high molecular weight and viscosity may be obtainedwhich are soluble in organic solvents such as toluene and acetone. Ifdesired, the polymerization may be carried to the point where theproduct is still soluble but is heat convertible; that is, it can beconverted by heat alone to a tack-free resinous solid which is notsoluble in most organic solvents.

The polymerization of organo-siloxanes by phosphorus pentoxide orphosphoric acid is probably accomplished by a combination of dehydration of hydroxyl groups and by rearrangement v of Si--O--Si groups.Phosphorus pentoxide and phosphoric acid are effective dehydratingagents and probably promote condensation of the hydrolyzed silicaneswherever active hydroxyl groups exist. In addition, they catalyze therearrangement of the extremely stable Si-O--S groups so that largermolecules are formed even when the siloxane is substantially free ofactive functional groups. In any event, we have found that phosphoruspentoxide and phosphoric acid are in general greatly superior to otherpolymerization catalysts both as to their eifect upon the speed ofpolymerization and upon the properties of the resulting products.

Reference should be had to the following examples for a betterunderstanding of our invention.

Example 1 A sample of trimeric phenyl ethyl silicone was heated to about180 C. and 1.5% of itsweight of phosphoric acid was added with stirring.The mixture was kept at 180190 C. until the viscosity of a 50% solutionof the product in toluene at 25 C. reached 50 centipoises. Thephosphoric acid was removed by washing with excess calcium hydroxide,leaving a toluene solution which served as an excellent coatingcomposition for glass fibre tape, the toluene evaporating upon theapplication of heat and-depositing a phenyl ethyl silicone coating thatbecame infusible and adherent upon further heating in the neighborhoodof 200 C: to 250 C. and remained tough and flexible after many hours atthese temperatures.

Example 2 A sample of butyltriethoxysilicane was hydrolyzed in thepresence of nitric acid. The nitric acid was removed by washing from thehydrolyzed product. Phosphoric anhydride was added to a portion of theproduct. The mixture was then heated for 24 hours at about C. An

extremely viscous liquid was produced whose molecular weight was foundto be 1650.

Example 3 After two and one-half hours with heat and under vacuum, theviscosity of the fluid was 67.3 seconds. Further heating under vacuumfor another 24 hours produced a material having only slight flow at roomtemperature.

Example 4 A sample of dibutyldiethoxysilicane was treated in the samemanner as the dimethyldiethoxysilicane in Example 3. Before the additionof phosphorus pentoxide the hydrolyzed product had a viscosity of 46.8Saybolt seconds. At the end of the two and one-half hours of heating inthe presence of phosphorus pentoxide its viscosity was 422 Sayboltseconds which increased to 1120 Saybolt seconds after further heatingfor 24 hours. Another sample of dibutyldiethoxysilicane was hydrolyzedwith alcohol and hydrochloric acid to an oily liquid. This liquid washeld at 100 C. for 13 hours. Itsviscosity was then determined to be 276Saybolt seconds as compared with the 1120 Saybolt seconds of the oiltreated wtih phosphorus pentoxide.

Example 5 Example 6 To dimethyldiethoxysilicane was added 5% sulphuricacid in an amount sufllcient to give a slight excess of the theoreticalwater required for hydrolysis. Acid and alcohol were washed out withwater. The resultant oil had a viscosity of 6 centistokes at 30 C. Aportion of this was then treated with of its volume of 85% phosphoricacid and' was heated to 125 C. for one hour with stirring. Forty-eighthours later this oil was washed with water, dilute ammonia, and thenagain with water; residual water was driven ofi with heat. The viscosityof the final liquid was 1730 centistokes at 30 C.

Example 7 Amixture was prepared consisting of 70 mol per centmonomethyltriethoxysilicane'and 30 mol per centtrimethylmonoethoxysilicane. This was dropped into half its volume of 2N hydrochloric acid while the temperature was held at 0 C. The mixturewas stirred during this addition. The mixture was then refluxed for 24hours. It was then thrown into a large volume of water and washed freeof acid. It was then taken up in benzene and refluxed with a water trapattached to the condenser. When no more water could be eliminated asample was removed and heated to 175 C. for 30 hours. The sampleremained liquid. To the remainder of the benzene solution there wasadded about 0.2% (based on the silicone content) of 85% phosphoric acid.Upon resuming the refluxing about 2% (based on solids) of water waseliminated within two hours. A sample of this material set to a resinoussolid in two hours at 150 C.

' Example 8 A mixture of ethyl silicon trichloride,'phenyl ethyl silicondichloride and diphenyl ethyl silicon monochloride in the molar ratio of1-8-2 respectively was dissolved in ether and hydrolyzed by mixing withwater. The ether solution of the resulting copolymer was washed free ofhydrochloric acid, and the ether removed by distillation. The resultingether free copolymer was V, 6 then polymerized with 2% by weight of 85%HaPO4 while blowing with steam. After 30 hours, the product was aresinous tacky material, soluble in toluene and having a viscosity insolution -of 420 centistokes at 25 0. Applied from a toluene solution toglass fibre tape it dried (after removal of solvent) in 3 hours ofbaking at 250 C.

' to a heat resistant, tack-free resin.

v Example 9 A mixture of ethyl silicon triohloride, phenyl silicontrichloride, phenyl ethyl silicon dichloride, diphenyl silicondichloride, diethyl silicon dichloride and diphenyl ethyl siliconmonochlo= ride (prepared by reaction of silicon tetrachloride, phenylmagnesium chloride and ethyl magnesium chloride in molar ratio of 1-1-1at 20 C.) was dissolved in ether and hydrolyzed with water. The ethersolution was washed free of acid and the ether removed byv distillation.The resulting copolymer material was polymerized to a viscous, tackymaterial by heating at 220 C. with .2% by weight of 85% HaPO4 whileblowing with steam. The material was soluble in toluene and when appliedfrom a toluene solution to glass fibre tape it dried (after removal ofsolvent) within a few hours of baking at- 250 C. to a heat resistanttack-free resin.

In addition to the examples given above, the condensed hydrolysisproducts o f diethyl silicon dichloride, ,diamyldiethoxysilicane,dibenzyldi ethoxysilicane, ethyltriethoxysilicane andamyltriethoxysilicane may be polymerized byrour method. Besides thesestraight mono and diorgano-substituted hydrolysis products, numerouscopolymers containing on theaverag'e of from less than one upto but notincluding three radicals per silicon atom have been polymerized inaccordance with this invention. These copolymers were prepared by thecohydrolysis and co-condensation of mixtures of diiferently substitutedhydrolyzable silicanes obtained directly a mixtures from the Grignardreaction of an organ-magnesium halide on silicon tetrachloride or ethylorthosilicate or prepared by mixing different silicanes of fair degreeof purity to give mixtures of desired constituents in predeterminedquantities. Among the silicanes employed to ac-l" complish the latterwere silicon tetrachloride, ethyl orthosilicate,methyltriethoxysilicane, dimethyldiethoxysilicane,trimethylethoxysilicane, phenylmethyldiethoxysilicane,phenyldimethylethoxysilicane, phenyltriethoxysilicane,diphenyldiethoxysilicane. ethyltriethoxysilicane, die thyl silicondichloride, phenyl ethyl silicon dichloride, =butyltriethoxysilicane,vdibutyldiethoxysilicane, benzyltriethoxysilicane,dibenzyldiethoxysilicane and others.

Our invention is applicable to any organo-silicon oxide polymer havingon the average less than three organic radicals attached to each siliconatom through carbon atoms. The unusual properties of these polymers aredue primarily to the Si-O-Si groups present therein and to the organicradicals attached. to the silicon atoms. The kind and number of organicradicals attached to silicon do not affect the fundamental behaviorofthe polymers, but only modify certain particular properties thereof.Besides the organic radicals already disclosed such radicals may beprescut as propyl, isopropyl, amyl, hexyl, heptyl to octadecyl andhigher; alicyclic radicals such as cyclopentyl, cyclohexyl, etc.; aryland alkaryl radicals such as monoand poly-alkyl phenyls as tolyl, xylyl,mesityl, mono-, di-, and tri-etbyl phenyls, mono-, di-, and tri-propylphenyis, etc.; naphthyl, monoand poly-alkyl naphthyls as methylnaphthyl, diethyl naphthyls, tri-propyl naphthyl, etc.;tetrahydro-naphthyl, anthracyl,

etc.; aralkyl such as benzyl, phenylethyl, etc.;-

alkenyl such as mcthallyl. ally], etc.

The new polymers may be used for various purposes. For example, they areexcellent coatings merized to complete insoiubility and infusibility.

In the latter state they have good mechanical characteristics and goodelectrical properties at room temperature, all of which are retained attemperatures above those at which prior coating materials break down anddeteriorate. The new polymers are relatively non-flammable and arelikewise superior to prior coatings in that under extreme conditions oftemperature, etc. there is little tendency to carbonize.

In making use of the new polymers for impregnating tapes and otherfibrous materials for electrical insulation the polymerization iscarried out until the material has attained the sticky, viscousheat-convertible state just short of insolubility. Then, if desired, theacid may be removed by neutralization with alkali such as sodiumhydroxide or calcium hydroxide. The alkali, when added in excess, alsoserves to remove impurities that may be.

present such as iron. etc. The neutralized product is dissolved intoluene or other suitable solvent. The solution is applied by dipping,brushing or spraying, followed by evaporation of the solvent. Severalapplications of the solution may be required to produce a coating ofsufficient thickness. -When the solvent has completely evaporated, thecoated article is baked for several hours at a temperature preferablybetween 200 C. and 300 C. until the viscous polymeric mixture isconverted to a tack-free coating. With the phenyl ethyl siliconepolymers, this condition is attained by baking for about 36 hours whilethe temperature is slowly raised from about 200 C. to about 260 C. Otherorgano-silicon polymers within the scope of our invention may requiredifferent temperatures and times, but such conditions are readilydetermined by trial.

In addition to the use of the new polymers in the field of electricalinsulation, there are many others for which these polymers at varioustages of polymerization are eminentl adapted particularly in thosestages prior to heat convertibility. In these thermally stable stages,they may be used as hydraulic fluids, liquid insulating media, thermalexpansion fluids, water-proofing agents, etc

Their resistance to high temperature, their electrical insulatingproperties, low freezing points and low vapor pressure adapt them tomany diversified industrial applications.

We claim:

1. The method of polymerizing substantially completely dehydrated liquidpolymers consisting of a polymeric diorgano siloXane in which one of thetwo organic radicals attached to each silicon atom is an alkyl radical,and the other organic radical is selected from the class consisting ofalkyl and aryl radicals, which comprises adding to said polymers anagent selected from the class consisting of phosphorous pentoxide andphosphoric acid, and maintaining said agent in reactive relationshipwith said polymer at a temperature below 250 C. until an increase inviscosity is effected.

2. The method of polymerizing substantially completely dehydrated liquidpolymers consisting of a polymeric diorgano siloxane in which one of thetwo organic radicals attached to each silicon atom is an alkyl radical,and the other organic radical is selected from the class consisting ofalkyl and aryl radicals, which comprises adding to said polymers anagent selected from the class consisting of phosphorous pentoxide andphosphoric acid, and maintaining said agent in reactive relationshipwith said polymers at a temperature between C. and 250 C. until anincrease in viscosity is effected.

3. The method of polymerizing substantially completely dehydrated liquidpolymers consisting of a polymeric dimethyl siloxane which comprisesadding to said polymers an agent selected from the class consisting ofphosphorous pentoxide and phosphoric acid, and maintaining said agent inreactive relationship with said polymers at a temperature below 250 C.until an increase in viscosity is effected.

4. The method of polymerizing substantially completely dehydrated liquidpolymers consisting of a polymeric dimethyl siloxane which comprisesadding to said polymers an agent selected from the class consisting ofphosphorous pentoxide and phosphoric acid, and maintaining said agent inreactive relationship with said polymers at atemperature between 100 C.and 250" C. until an increase in viscosity is effected.

5. The method of polymerizing substantially completely dehydrated liquidpolymers consisting of a polymeric dimethyi siloxane which comprisesadding to said polymers an agent selected ROB ROY MGGREGOR. EARL LEATHENWAR/RICK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,371,068 Rochow Mar. 6, 19452,258,220 Rochow Oct. 7, 1941 FOREIGN PATENTS Number Country a 7 Date113,708 Australia Sept. 4, 1941 OTHER REFERENCES Beilstein, HandbuchderOrgan .Chem., vol. 4, page 627, 4th ed. (1922). 4 Ellis, The Chemistryof Synthetic Resins, vol. I, 1935 (Reinhold), page 54 Robison et al.,Tr. J. Chem. Soc., London, vol.

105, 1914, pages 40 to 43.

Certificate of Correction Patent No. 2,435,147..

ROB ROY MCGREGOR ET AL.

It is hereby certified that errors appear in the printed specificationof the above numbered patent requiring correction as follows: Column 4,line 20, for Si-O-S read Si-O-St'; Column 6, line 44, fororgan-magnesium read organ'o-magnesium; and that the said LettersPatent. should be read with these corrections therein that the same mayconform to the record of the case in the Patent Office.

Signed and sealed this 20th day of April, A. D. 1948.

THOMAS F. MURPHY,

Assistant (Zommissz'oner of Patents.

January 27, 1948.

